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Y'know, I'd thought of using a mechanic like that before, an the question of a crit never occured to me. There are several ways you could go with it. You could look at the number of hits determining damage, so if the first attack is a hit, the second is only to determine how much damage is done - in which case, only the first attack determines whether the hit is a crit. If the second attack hits, and crits, that'd be a crit, also. But a 1st attack hit, 2nd crit, would just be a regular hit for the higher damage figure. You could look at both attack rolls as alternate attack rolls on one power, so if either crits, the whole power crits.You could look at them separately, so if one crits, it's d6 is maximized, and if both crit both d6's are maximized - the problem with that is that other crit effects would both be doubled up in the unlikely event you got two crits. So if you were 8th level and did +2d10 on a crit, you'd do 6+d6 +2d10 on a single crit, and 12 + 4d10 if both rolls were crits. At that point, you're getting awefully close to them just being two separate attacks.